1. Field of the Invention
This invention relates to the fabrication of semiconductor structures having atomic dimensions, generally in the range from an Angstrom (10.sup.-10 meter) to a nanometer (10.sup.-9 meter) and above and, more specifically, to fabrication of such structures using both the surface chemistry involving the atoms on the semiconductor surface and the surface reconstruction which involves the reordering of the surface atoms.
2. Brief Description of the Prior Art
The construction of sub-micron size structures for electronic devices with rapid lithographic techniques is of extreme importance for higher density semiconductor device architectures. For the ultimate semiconductor device structure, manipulation of atoms on a surface with a high degree of control and with rapid lithographic techniques is required. Current spatial resolution in photon lithography, where light is used to expose and develop a photosensitive polymer (resist), is a result of the source wavelength, the wafer-mask distance, the lens system and the spatial frequency of the object. For electron-beam resists, the spatial resolution is also limited by phenomena such as the spatial extent of secondary electron generation within the resist material. Moreover, for electron-beam lithography, a large flux of electrons may be required in the lithographic process as explained by W. Runyun and K. Bean, Semiconductor Integrated Circuit Processing Technology, Addison-Wesley, New York (1990).
The investigation of the surface chemistry of semiconductor (crystal) surfaces has been conducted for in excess of 30 years. From such work, the surface chemistry of various adsorbates with these semiconductors has been elucidated.
Semiconductor surfaces are unique in that an atomically "clean" surface has unsaturated valences ("dangling bonds") present on the surface. Such bonds, which present themselves in a well-ordered registry with the surface atoms, are thought to be highly reactive with almost any molecular/atomic species subjected to interactions with such bonds. Upon adsorption of a species to these surface dangling bonds, the chemical reactivity of the bond is reduced or "passivated". Such passivation has profound effects on the electrical performance of semiconductor devices as discussed in the above noted Runyan et al. reference and by Y. Nemirovsky, Journal of Vacuum Science Technology, A8 (1990), page 1185.
An important example of such passivation is the use of hydrogen passivated surfaces to preclude surface site reactivity on silicon single crystal surfaces. Through the use of ultra-high vacuum as discussed by J. J. Bolland in Physical Review Letters, 65 (1990), page 3325 or atmospheric wet-chemical techniques as discussed by G. S. Higashi et al. in Applied Physics Letters 56 (1990) at page 656 and P. Dumas et al. in Physical Review Letters 65 (1990) at page 1124, hydrogen passivated silicon surfaces can now be routinely prepared. Such surfaces are characterized by well-ordered arrays of passivated dangling-bonds in precise spatial registry with the surface atomic structure.
It has also been shown that adsorbed hydrogen is also sensitive to electron stimulated desorption (ESD) effects on single crystal silicon surfaces. Thus, hydrogen atoms can be deposited over the silicon surface and removed by using electron bombardment as discussed by R. M. Wallace et al., Surface Science 239 (1990) at page 1, E. C. Ekwelundu et al., Surface Science 215 (1989) at page 91 and C. F. Corallo et al., Surface Interface Anal. 12 (1988) at page 297.
Similarly, the manipulation of atoms at the surface of semiconductors has also been investigated, largely through the use of the scanning tunneling microscope. Experiments have demonstrated electron beam induced chemistry and (tip-induced) electron stimulated desorption of hydrogen from such passivated surfaces as discussed by R. S. Becker et al., Physical Review Letters 65 (1990) at page 1917. The main practical difficulty with the use of the scanning tunneling microscope approach is that the method is much too slow for a commercial manufacturing process.
It has also been shown that steric effects of impinging molecules on well-ordered semiconductor surfaces permit specific adsorbed orientations of the molecule on the surface. As an example, the adsorption of unsaturated hydrocarbons, such as ethylene, on the Si(100) surface has shown that such species prefer a specific orientation of the surface, as shown in L. Clements et al., Surface Science 268 (1992) at page 205. Such specific orientations are thought to be a result of the chemical interaction of the adsorbate with the surface dangling bond structure and are thus directly associated with the surface atomic structure. Thus, by choosing the impinging molecule for film growth and the substrate surface, which has a known surface reconstruction, one can, in principal, dictate the orientation of the film purely by surface chemistry.